The present invention relates to a method and apparatus for inspecting the filled state of via-holes filled with fillers, which are formed to electrically connect circuits on the front and back sides of a printed circuit board (a ceramic printed circuit board included).
An inspection method for via-holes of a translucent printed circuit board, which is made of polyimide, with copper circuits is indicated in Japanese Patent Application Laid-Open No. 61-17049. A detection method for a defective filling state of general fillers is indicated in Japanese Patent Application Laid-Open No. 55-118753.
Detection methods for the height of an object by measuring the shadow length of the object which is irradiated by light slantwise are indicated, for example, in Japanese Patent Application Laid-Open Nos. 60-22611 and 58-92904.
The techniques mentioned above cannot identify whether an object is protruded or sunk under a datum plane nor detect a defective filling state of fillers in each via-hole.